1) Auto white balance seems to yield a slightly greenish cast in some scenes. That is very well documented by the CameraStore review on Youtube

2) The size of the RAW-files

3) The (minor) focus problems D800 seems to have.

D600 was originally on the top of my list. But using Dpreview`s jpg quality comparison, it seems that MK III was more detailed at all ISO. Besides, the video quality was MUCH better on the MK III.

So when I got the huge price reduction on MK III, it was a no brainer.

I have been using this camera since last June. You will love it. I still get excited over how reliable and responsive it is. Just came back from concert with just about the worst conditions. Terrible lighting, dark skin singers, some in front of a brightly lit canvas, 12800 iso f:2.0 pr 2.8 to get decent shutter speed (1/60), yet the AF nailed it very consistently, and the files out of the camera are really good. This camera really behaves well in extrem conditions.